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Very low-grade metamorphism of Rheno-Hercynian allochthons (Variscides, Germany): facts and tectonic consequences.
- Source :
-
International Journal of Earth Sciences . Jul2012, Vol. 101 Issue 5, p1229-1252. 24p. 1 Diagram, 2 Charts, 7 Graphs, 4 Maps. - Publication Year :
- 2012
-
Abstract
- The Hörre Belt in the SE part of the Rhenish Massif has been regarded as autochthonous because of the apparent lack of metamorphic inversion. We have performed a K-white mica study using powder X-ray diffraction derived Kübler Index (KI) and K-white mica b cell dimension, and the spectrally derived wavelength of the 2,200 nm absorption feature ('2200wvl') of supposedly allochthonous units and the underlying par-autochthon. KI reveals a slight, but significant inversion of metamorphic grade, which shows that the Hörre Belt and the Hessische Schieferserie adjacent to the South were emplaced by thrusting after they had acquired peak metamorphism ( M) in deeper parts of the orogenic wedge. Only in the westernmost part of the study area, the par-autochthon and the allochthon show the same grade of anchizonal metamorphism. This observation, together with K-white mica b cell dimensions <9.000 Å and 2200wvl <2,204 nm, suggests a second, low-pressure metamorphism M subsequent to the emplacement of the allochthon. This is supported by an anomaly of published conodont alteration index data. Our results expand the original width of the Rheno-Hercynian passive margin to at least 580, more probably to 670 or even 750 km. Palinspastic restoration also reveals that the Givetian to Early Carboniferous volcanic belt of the Lahn/Dill area is not only younger than the Emsian MORB-type lavas of the Rheno-Hercynian ocean, but was also separated, from the latter, by a largely non-volcanic belt of at least c. 220 km width. Apparently, the Givetian to Early Carboniferous volcanic episodes were unrelated to the Rheno-Hercynian drift stage. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 14373254
- Volume :
- 101
- Issue :
- 5
- Database :
- Academic Search Index
- Journal :
- International Journal of Earth Sciences
- Publication Type :
- Academic Journal
- Accession number :
- 76311984
- Full Text :
- https://doi.org/10.1007/s00531-011-0718-3